Tokkai Hei 4-366049 published by the Japanese Patent Office in 1992 discloses a toroidal continuously variable transmission for vehicles wherein the ration of the rotation speed of an input disk to the rotation speed of an output disk, i.e., a speed ratio, is continuously varied by varying the gyration angle of a pair of power rollers gripped between the input disk and output disk. The power rollers are respectively supported by trunnions at a position facing each other.
These trunnions must be rotated synchronously. In this context, Tokkai Hei 7-253145 published by the Japanese Patent Office in 1995 discloses a technique wherein a pulley is formed in the trunnions, and the trunnions are synchronously rotated by looping an endless wire around a pulley groove of the pulley. The slipping of the endless wire in the circumferential direction is prevented by engaging a large diameter part of the endless wire with a notch formed in a pulley groove. Therefore, in order to accurately synchronize the gyration angle of the trunnions, the notch must be formed precisely in the circumferential direction.
However, when the trunnions are formed by forging, casting or sintering, the precision of the notch is poor.
Therefore, the notch has to be machined after forming, but if the notch is machined by driving a tool in the axial direction while the trunnion is rotated around its rotation axis as the notch runs in a circumferential direction, the number of indexing steps of machining positions and positioning steps increases and the productivity declines.
It is therefore an object of this invention to machine the notch which engages with the large diameter part of the endless wire to a high precision without reducing productivity.
In order to achieve the above object, this invention provides a trunnion of a toroidal continuously variable transmission and a manufacturing process for the trunnion. The trunnion comprises a support having a hole therethrough comprising a pulley with a pulley groove and a notch crossing the pulley groove, a first shaft on the top of the support, and a second shaft part on the bottom of the support that is coaxial with the first shaft part, the notch comprising an arc portion and two straight portions, one of the straight portion being formed on one side of the arc portion and the other of the straight portion being formed on the other side of the arc portion. The process comprises forming said pulley groove and said notch by forging, casting or sintering, aligning a rotary tool for machining a flat surface by a blade provided on an end face so as to face a boundary interface between the pulley groove and notch, and rotating the tool while moving the tool forward in the axial direction of the tool so as to cut the boundary interface to a predetermined position.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.